Micropropagation of Three "Pyrus" Rootstocks.

Expiants of three rootstocks Pyrus cummunis L. "Old Home" x "Farmingdale" (OHxF 69, 40 and 87) were initiated from branches of field-grown trees on MS medium, MS one-half the NH4N03 and KN03 concentrations medium and Lepoivre added with BA and IBA. MS one-half the NH4N03 and KM), concentrations medium with BA and Lepoivre with BA and IBA seem to be the best media for the initiation of the three rootstocks. The best multiplication medium for the three cultivars is the MS medium one-half the NH4NO3 and KNO3 concentrations with 8.8 jiM BA or added with 0.25 or 0.5 (J '1 IBA. The subculture's number increases the shoot explant's number but it also increases the hyperhydricity percentage. Pyrus communis OHxF seems to be sensitive to nitrate. In vitro rooting of rootstocks requires the use of well-developed micro buds and an adequate auxinic pre-treatment of each rootstock. IBA at 10 ji'l seems to be the most suitable auxin for the rooting of the three rootstocks, while the dilution of the basic medium MS seems to be essential for the improvement of the rooting. A phase of obscurity appears to be compulsory for OHxF69 but not for OHxF40 and OHxF87. Only rooted and developed plantlets survived greenhouse acclimatization.